Status Updates From Contingency and Convergence...

In essence, resolving the evolutionary history of brains is the first step toward constructing a phylogeny of minds.

Deep homologs essentially act as triggers that merely allow traits like eyes or limbs to develop or not, but they not specify how these traits should develop in three-dimensional space. Thus, contra Gould, the repeated activation of deep homologs like Pax6 does not convert these cases of convergence into parallelisms.

The challenge is to distinguish iterations indicative of deeper modal robustness from those that are evidence for shallower degrees of replicability. If one remains unconvinced that his distinction can be drawn, than one must accordingly resign to the fact that the contingency debate is permanently underdetermined by convergence data - and that we must look elsewhere, perhaps beyond Earth, to make any headway on it.

Dozens of coevolutionary convergences on flower and ant morphologies offer far weaker evidence against the RCT than do convergences that are fewer in number but that can be shown to arise from broad physicochemical constraints on life. For the latter do not hinge on the peculiar - and singularly evolved - developmental parameters of particular lineages.

At bottom the contingency debate is not a relative frequency dispute about evolutionary repetition per se - rather, it is a dispute over the nature and causes of those repetitions.

When we take into account the evidence for an extremely early origin of life, the repeated evolution of free-living cells, the cosmic ubiquity of the chemical building blocks of life, and models of code convergence under heavy horizontal gene transfer, a strong case can be made for the cosmic imperative of life thesis, even if a single alien microbe has yet to be found.

Macroscopic life forms are far more likely to have their genomes analyzed; yet all macroscopic organisms are eukaryotes, a relatively young evolutionary branch of the incumbent tree, and thus not where we would expect to find alternative codes. Until a far greater proportion of microbial diversity is analyzed, we cannot be sure that there are no tiny aliens living among us.

Unlike the Umwelt, which is likely to have evolved in positive feedback with image-forming sensory modalities and motor systems, the evolution of cumulative technological capacities appears to occur only when a suite of largely orthogonal factors, each with a low probability of occurring, are simultaneously in place.

The collision that killed the dinosaurs is what Powell calls a non-merit based selective event because it picks winners that would otherwise not have an adaptive advantage. Gould believes such events send evolution down an otherwise unpredictable path. Powell claRifies this idea. Only criticism: analogies and examples which would help orient the reader are unhelpfully given at the end of a section.

Good so far, nice balance between science and philosophy. Enjoyed learning about the speed at which life arrived when conditions on earth were habitual.